Manufacture of cellulose from cornstalks



Feb. 23, 1932. E. R. DARLING 1,846,511

MANUFACTURE OF CELLULQSE FROM CORNSTALKS Fil ed Dec. 13, 1928 19 STACK OF BALED 1/ CQRNSTALKS OLIVER FILTER l FIBERS 16 Z BALE BREAKER I 17 3/{WASHER| DEcKER 18 WATER FILTER .121 SHREDDER RECEIVER F BLEQE soLUTIoN j REFORTIFY gg FILTER OH AND RECOVERY 01% NWBSOS RETURN TO PROCESS SOFTENING FINISHED PULP TANK (5 TIMES) STOCK 20 @EW A B 19 13 8 AFTER 5 EXTRACTIONS 1/ I SEND TO RECOVERY T "C|RCU| AT|NG DEPARTMENT 0 DIGESTER l 6 TO REGULAR PAPER /PRoc Ess PUMP o J, J4

9 K I o PUMP RECEVING TANK BLEAcI-I coRN STALK PAPER PULP HYDROLYZER FINAL PRODUCT Patented Feb. 23, 1932 UNITED STATES PATENT OFFICE ELTON R. DARLING, OF DANVILLE, ILLINOIS, ASSIG-NOIR, BY MmNE CORNSTALK PRODUCTS COMP-ANY, INC.

DELAWARE ASSIGNMENTS, TO

OF NEW YORK, N. Y., A CORPORA'I'IGN OF MANUFACTURE OF CELLULOSE FROM CORNSTALKS Application filed December 13, 1928. Serial No. 325,897.

The present invention relates to improvements in the manufacture of cellulose from plants of annual growth, as, for example, from cornstalks (maize).

My invention represents an improvement in the art of treating cornstalks for the separation of cellulose therefrom, and the present application is a continuation, in part, of m co-pending applications Serial Nos. 313,190, 313,191, 325,894, and 287,651.

Among the objects of my invention are the following:

1. The efficient separation of the cellulose from the pentosans and lignins contained in the natural cornstalks;

2. The utilization of the digestion liquors for further operations in the process;

3. The efiicient treatment of the cornstalks prior to the digestion step so that the same may be more readily treated and the recovery of cellulose therefrom rendered more effective 4. To carry out the digestion of the comminuted cornstalks in a digester in which the entire mass of material, including the digestion liquor, is kept in constant circulation while maintained under superatmospheric pressure;

5. To separate the liberated cellulosic fiber from the liquors in which they have been boiled, followed by a washing operation, combining the liquors resulting from said washing operation and returning them to 'the process a predetermined number of times, following which the values therein contained are recovered; and

6. To produce a finished paper pulp ready for use for conversion into paper articles from cellulose contained in cornstalks in an operation which, at its maximum, does not require a longer time than eight hours.

Other objects will appear in connection with the drawing and the description of the process which forms a part of the present specification.

The drawing referred to is a diagrammatic flow-sheet which shows the sequence of the operations as they are described in the specification, and also by appropriate in dicia. shows the flow of material from start to finish and the cross flow and return flow of the various liquors, filtrates and other products resulting from the operations. No attempt has been made in the drawing to illustrate any particular apparatus, except in the form of a diagram thereof, and I would, therefore, have it understood that my process y does not have apparatus limitations, except in so far as the sequence of operations is to be substantially as that herein described. In the said drawing, the operation is shown as begining with a stack of baled cornstalks Which are kept on hand at the plant where the operations are to be carried out, and the process comes to its completion, as far as the present invention is concerned, at the point where the finished pulp stock is ready either for the regular paper machine or to be sent to the bleachers or hydraters. I have illustrated on the said drawing a number of steps which follow after the process of my inventionhas come to its end, these steps being designated by the letters A and B on the said drawing. However, the manufacture of paper or the bleaching of the paper or the hydration thereof or the conversion of the cellulose into final products, such as cellulose esters, does not form a part of the present invention, but is illustrated on the said drawing as illustrative and not as a limitation.

The manufacture of cellulose pulp or paper pulp from cornstalks begins with the harvesting of the stalks which may be accomplished either by hand or better by appropriate machinery, which, after removing the cars from the cornstalks, compresses the same and bales them so that they may be transported into the storeyard of the conversion stalks furnishes the same to the plant in a rough shredded condition in bales.

By this rough shredded condition, I mean that the stalks themselves are split longitudinally and may be broken into lengths less than their original length but I do not mean that they are at all finely divided.

The first operation in the process in accordance with my present invention is the bale-breaking operation. This is carried out in the bale breaker 2, which is of ordinary construction and serves to pull the stalks out of the bales and to loosen the same so that they may be then transferred to the wash tank 3. In this wash tank they are mechanically agitated, preferably being rotated, Water being constantly removed and added to the washer. There is no attempt made during this operation to break up the stalks further than in the bales, only to separate the stalks from each other so that water ma have access to all parts of them.

his operation, in which preferably the water runs countercurrent to the flow of the stalks, serves to remove a great deal of the adhering sand, insects, moulds, and plant dbris that is not desired in the final product, and which would interfere with the effective carrying out of the process. This washing also removes from the stalks a considerable part of the foreign content and water-soluble constituents.

After the stalks have been washed, they are transferred to the shredder 4, which may take the form of what is known as a J efi'ery mill. In this shredder or mill the stalks are reduced to a fine condition, being shredded to about the consistency of excelsior but with no fiber longer than in length, and usually on the order of from A" to A This shredding operation also serves to liberate a further quantity of adhering dirt, sand and other dbris which failed of removal in the first washing step, and for this reason the finely shredded cornstalks are then transferred to the second washer 5 where again the washing is carried out by a countercurrent of clear water and further quantities of solubles are removed from the stalks.

The shredded cornstalk material is now subjected to a step which, to my knowledge, has never been applied before in the production of cellulose from this type of material, namely, the shredded cornstalk material is placed into a tank 6 which I have designed as a softening tank wherein the stock of cellu losic material is subjected to treatment with a solution containing substantially 1% free sodium hydroxide and of 1% of sodium sulphite. The amount of liquor used is approximately 10 parts of liquor to one part of shredded cellulosic material, this proportion, however, being predicated and adjusted according to the amount of moisture remaining in the shredded cellulosic material after it comes from the washer 5. Inasmuch as the cellulosic material is removed from the washer 5 and merely allowed to drain, it will usually contain an amount of water which is fairly constant and which can be ascertained by the usual laboratory methods so that a proper correction for the amount of softening liquor to be added may be made. The cellulosic material at this stage is in the form of a rough pulp or suspension of crude cornstalk fibers in the softening liquor. While suspended in this liquor, the cellulosic material is subjected to a slight cooking operation, which corresponds to the temperature and is equivalent to ten pounds of pressure above that of the atmosphere.

In order to accomplish this, the softening is carried out in a closed tank, but the suspended cellulosic pulp remains in this softening tank only long enough to soften the same so that it becomes possible to transport the same for the further operations by means of a centrifugal or rotatory pump. This softening operation renders the fibers very soft and flexible and they may then be pumped in the suspended condition into the digestion tank 8 by means of the pump 7 it being understood that the entire contents of the softening tank, including the liquor, is thus placed into the digestion tank.

Thisdigestion tank, as I prefer to employ it, consists of a metallic cylindrical tank having a conical bottom which terminates in a relatively large pipe, which, leaving the lowest portion of the cone, makes a large 180 U-turn and leads into a pump 9 which discharging into a vertical pipe 10 is capable of pumping the contents out of the bottom of tank 8 back into the top of the same substantially as shown by the arrows shown in connection with the tank 8 in the drawing.

This tank is also provided with the usual pressure relief valves and with pressure gages, and the pipe 10 is surrounded for a substantial portion of its length with a steam jacket 11 through which superheated steam is passed while the operation is in progress. By reason of the circulation of the entire pulp through pump 9 and the pipe 10, and as the result of the heat transmitted to the pulp flowing through pipe 10 from the jacket 11. the pulp will gradually become heated to the boiling point and as the digester is tightly closed, superatmospheric pressure will be built up therein by the resulting steam.

I prefer to operate at a pressure equivalent to ten pounds in excess of that of the atmosphere at the start and to build this pressure up gradually during the operation until the pressure of substantially thirty pounds per.square inch is reached, this being the optimum pressure for carrying out the process. It will be noted that this boiling operation under pressure in digester 8 is carried -lulosic constituents of the cornstalk ess, and, in fact, the entire out with the liquor which has been added to the cellulosic material in the softening tank, and which, as already stated, contains substantially 1% of sodium hydroxide and of 1% of sodium sulphite. The purpose of the sulphite is to furnish a reducing agent so as to preclude undue oxidation of the celmaterial, as any oxidizing tendency would expend itself upon the oxidation of the sodium sulphite instead. I

The constant circulation of the cellulosic material suspended inthe digester 8 by means of the pump 9 and the heating of the same while passing upwardly through the pipe 10 prevents packing of the material in the digesterand, also, by reason of the trituration of the fibers against each other materially aids in the liberation of the cellulose fibers and in the solution of the pentosans and lignin materials which serve tg cement the fibers together in the stalks. This operation of circulating and boiling simultaneously obviates the necessity for the usual beater operation that ordinarily follows a digesting step in the process of making wood pulp or paper pulp, as heretofore practiced. I consider this an important step in the advance of this art, and have found that it materially contributes to the success of my process of liberating the cellulosic fibers from cornstalks, whereas other processes which differ from my process in employing a much more drastic treatment have failed because they have so severely injured the cellulosic fibers so as to render the same virtually useless.

I also wish it to be understood that the digestion operation, as above described, only lasts about two hours and not for from eight to twenty-four hours as is the case in fiber liberation from wood. Also, in my process the amount of sodium hydroxide is very much lower than in any other similar procproces's aims to preserve the cellulose in as nearly its natural condition and as free from oxidation as possible.

After the circulation and the digestion of the cornstalk cellulosic material in the digester 8 has been carried to its conclusion (from 30 to 40 minutes after final pressure has been reached), the circulating pump 9 is shut off and the valve 12 on the tank 8 is opened (after first blowing off the excess pressure on the tank through the discharge valve 13) into a receiving tank which should be large enough to hold the contents of several such digesters as the tank 8. This receiving tank is in communication with the pump 14, which is of such construction that it may pump the suspended cellulosic material, which is now practically pure cellulose suspended in a solution of pentosans and lignins in the cornstalks against considerable ead pressure to one of the upper stories of 18 serves as the factory where the suspension is subjected to a filtering operation to separate the 'cellu- Well known device and Widely used for filtration for such purposes. The solids collecting on the rotatory surface of the filter are not washed thereon but are merely scraped off by the usual doctor-blade and transferred by means of a spiral conveyor into a wash tank 16, where the fibers are mixed with water and agitated.

The fibers then pass to another filter 17 which, however, I prefer to have of the well known Decker type, where a separation into solids and liquids takes place. The Wash water from the Decker filter 17 is not thrown away but passes into a tank 18, which said tank also serves to receive the liquors that come from the Oliver filter 15. The tank a storage tank for the liquors, which liquors are re-used in the process by being conducted into the softening tank 6. The liquors titrated to determine the amount of sodium hydroxide contained in the same and if there is a deficiency, this is made up by the addition of suflicient caustic soda and sodium sulphite to bring the solution to a concentration of substantially 1% of NaOH and of 1% of Na so However, after this liquor has been returned to the process five times, it is not again returned but passes to a recovery department broadly designated by the figure 19, in which the liquor is treated for the recovery of pentosans and other valuable material according to the process disclosed in my copending applications Serial Nos. 289,088, 325,892, and 325,896. The solids removed from the Decker filter 17 are conveyed to a second Decker filter 1711 upon which they are washed by a spray of water, whereupon the fibers which'now represent fairly pure cellulose, are transferred to a tank 20 and stored therein. This constitutes what I please to call finished pulp stock. This finished pulp stock is of a grayish-green color and may be used directly for making paper pulp or may be made into paper. For instance, following the course designated by the letter A, the finished paper pulp stock may pass to a paper machine to be converted into a low grade paper, as, for example, wrapping paper. Al-

ternatively, following the course B, the said pulp may either go to a paper producing machine; go through a bleaching operation; or go through a hydra-ting operation so as to yield a final product which may be either bleached pulp, unbleached paper pulp, hydrated paper, or the raw material for the manufacture of viscose or cellulose esters, or for any other purpose for which cellulose might find application. I do not claim any part of the process beyond tank 20.

The outstanding advantages of my process reside in the fact that by the efficient treating, washing and shredding of the cornstalks a great deal of the undesirable material therein is removed. A further advantage resides in the fact that the cornstalk material, after the shredding, is given an initial softening bath which makes it possible thereafter to handle the material entirely by pumps, thereby obviating all manual handling. This obviously greatly reduces the cost of operation and makes the process capable of competing with wood pulp and other low grade cellulosic products, while, at the same time, yielding a cellulosic fiber much higher in alphacellulose and substantially free from oxycellulose. The sequence of the operations is substantially as that shown herein, although the exact type of apparatus used need not conform with the description herein given, as other known and standard filtering means may be used with equal effect. There are a number of efiicient bale-breakers and shredders on the market, and I may use any of the standard devices shown, although I do prefer to use the circulating type of digester, especially the one shown in co-pending application Serial No. 366,049, filed May 25, 1929. Instead of using sodiumhydroxide, it is, of course, possible to use potassium hydroxide or otassium sulphite instead of sodium sulphlte, although for purposes of cost, I prefer to use the sodium salts. The percentage of the strength of the solution may vary somewhat, although I do not attempt to use a solution stronger than 2% NaOH or stronger than A; of 1% of Na SO The pressure in the softening tank may vary between five and fifteen pounds, but is preferably kept at ten pounds, whereas the pressure in the digestion tank 8 starts at ten pounds and gradually builds up to thirty pounds, the thirty pounds pressure being attained after about twenty minutes of operation and not maintained much longer than ten minutes at the most. Carrying out the operation at higher pressures would result in a serious damage to the cellulose fibers and to degradation and to de-polymerization to the pentosans which are contained in the cornstalks and which represent a very valuable by-product.

I claim:

1. The process of preparing cellulose from cornstalks and similar annual plants which comprises coarsely shredding said plants, washing the same, further shredding and washing the same, subjecting the shredded product resulting from the said operations to a softening operation by heating with a solution containing an alkali and a reducin agent whereby a softened pumpable pulp 0 plant material results, pumping said pulp into a. digester together with the liquor employed for its softening and boiling it therein under super-atmospheric pressure until non-cellulosic constituents of said pulp have become dissolved.

2. The process of preparing cellulose from cornstalk and similar annual plants which comprises coarsely shredding said plants, washing the same, further shredding and washing the same, subjecting the shredded product resultin from said operations to a softening operation by heating with a solution containing sodium hydroxide and a reducing agent whereby a softened pumpable pulp of plant material results, pumping said pulp into a digester together with the liquor employed for its softening and boiling it therein under superatmospheric pressure until -non-cellulosic constituents of said pulp have become dissolved.

3. The process of preparing cellulose from cornstalks and similar annual plants which comprises coarsely shredding said plants, washing the same, further shredding and washing the same, subjecting the shredded product resulting from the said operations to a softening operation by heating with a solution containing sodium hydroxide and sodium sulphite whereby a softened pumpable pulp of plant material results, pumping said pulp into a digester together with the liquor employed for its softening and boiling it therein under superatmospheric pressure until non-cellulosic constituents of said pulp have become dissolved.

4. The process of manufacturing cellulose from cornstalks which comprises shredding said stalks, washing them with water, further shredding, again washing with water, heating the shredded stalk material with a softening solution comprising a small amount of an alkali and a still smaller amount of a reducing agent until a soft pumpable mass results, pumping said mass into a digester and boiling it therein under superatmospheric pressure until the non-cellulosic constituents of the cornstalk material become dissolved, and thereupon separating the thus liberated cellulose fibers of said material from the dissolved substances.

5. The process of manufacturing cellulose from cornstalks which comprises shredding said stalks, washing them with water, fur ther shredding, again washing with water, heating the shredded stalk material with a softening solution comprising a small amount of an alkali and a still smaller amount of a reducing agent until a soft pumpable mass results, pumping said mass into a digester and boiling it therein under superatmospheric pressure with constant circulation of said mass during the digestion until the noncellulosic constituents of the cornstalk material become dissolved, and thereupon separating the thus liberated cellulose fibers of said material from the dissolved substances.

6. The process of manufacturing cellulose from cornstalks which comprises shredding said stalks, washing them with water, further shredding, again washing with Water, heating the shredded stalk material with a softening solution comprising a small amount of sodium hydroxide and a still smaller amount of sodium sulphite until a soft pumpable mass results, pumping said mass into a digester and boiling it therein under superatmospheric pressure until the non-cellulosic constituents of the cornstalk material become dissolved, and thereupon separating the thus liberated cellulose fibers of said material from the dissolved substances.

7 The process of manufacturing cellulose from cornstalks which comprises shredding said stalks, washing them with water, further shredding, again washing with water, heating the shredded stalk material with a softening solution comprising a small amount of sodium) hydroxide and a still smaller amount of sodium sulphite until a soft pumpable mass results, pumping said mass into a digester and boiling it therein under superatmospheric pressure with constant circulation of said mass during the digestion until the non-cellulosic constituents of the cornstalk material become dissolved, and thereupon separating the thus liberated cellulose fibers of said material from the dissolved substances.

8. The process of manufacturing cellulose from cornstalks which comprises shredding said stalks, washing them in water, further shredding, again washing the same, heating them with a softening solution containing substantially 1% of sodium hydroxide and 1/ 10% of sodium sulphite until a soft pumpable mass results, transferring said mass together with the softening solution into a digester and digesting it therein at superatmospheric pressure until the non-cellulosic constituents of the mass become dissolved and the cellulose fibers liberated, and thereupon separating the "fibers from the solution of noncellulosic material.

9. The process of manufacturing cellulose from cornstalks which comprises shredding said stalks, washing them in water, further shredding, again washing the same, heating them with a softening solution containing substantially 1% of sodium hydroxide and 1/10% of sodium sulphite until a soft pumpable mass results, transferring said mass together with the softening solution into a digester and digesting it therein at superatmospheric pressure with constant circulation of said mass during the digestion until the noncellulosic constituents of the mass become dissolved and the cellulose fibers liberated, and thereupon separating the fibers from the solution 0 non-cellulosic material.

10. The process of manufacturing cellu-- of sodium sulphite until a soft lbs. pressure until the non-cellulosic constituents of the mass'become dissolved and the cellulose fibers liberated, and thereupon separating the fibers from the solution of noncellulosic material.

11. The process of manufacturing cellulose from cornstalks which comprises shredding said stalks, Washing them in water, further shredding, again washing the same, heating them with a softening solution containing substantially 1% of sodium hydroxide and 1/ 10% of sodium sulphite until a soft pumpable mass results, transferring said mass together with the softening solution into a digester and digesting it therein at 10 to 30 lbs. pressure with constant circulation of said mass during the digestion until the non-cellulosic constituents of the mass become dissolved and the cellulose fibers liberated, and thereupon separating the fibers from the solution of noncellulosic material. 12. The process of manufacturing cellulose from cornstalks which comprises subjecting comminuted and washed cornstalk material to a softening solution containing substantially 1% sodium hydroxide and 1/10% sodium sulphite at a temperature corresponding to 10 lbs. pressure above atmospheric, whereby a pumpable mass of softened cornstalk material results, transferring said mass together with the softening liquid to a circulating digester and digesting it therein at a pressure which starting with substantially 10 lbs. superatmospheric is gradually raised to not over 30 lbs. pressure during the digestion period, whereby noncellulosic materials dissolve and cellulose fibers are liberated, and thereupon separating the cellulose fibers from the solution of the non-cellulosic constituents.

13. In the process of manufacturing cellulose from cornstalks as described in claim 12, the step which comprises constantly circulating both the cornstalk mass and the digesting liquor during the digestion.

14. The process of manufacturin cellulose from cornstalks which comprises the step of digesting the same in shredded condition in a closed steam-tight digester with a solution adapted to liberate the fibers therefrom while continuously circulating the mixture of solution and shredded cornstalks during the digestion by withdrawing the mixture from the bottom of the di ester, heating the same, and reintroducing t e same into the top of the digester.

15. The process of manufacturing cellulose from cornstalks which comprises subjecting the same in shredded condition to the action of a solution of a substance capable of effecting fiber liberation therefrom while continuously circulating said liquor and cornstalks throu h a restricted area in which heat is transi erred to the solution.

In witness whereof, I have hereunto subscribed my name.

ELTON R. DARLING. 

